Re: [PATCH] fb: avoid possible deadlock caused by fb_set_suspend

Florian Tobias Schandinat
2011-09-02T16:46:49Z

Hi Bruno, Guennadi,

On 09/02/2011 04:06 PM, Guennadi Liakhovetski wrote:
> Hi Florian
>
> On Thu, 1 Sep 2011, Florian Tobias Schandinat wrote:
>
>> ping
>>
>> Guennadi, I really want this issue fixed. Please have a look at Bruno's patch
>> otherwise your driver might remain or get even more broken...
>>
>> I am scheduling Herton's patch for the next merge window.
>
> So, the patch looks simple and correct, when applied on top of
> http://marc.info/?l=linux-kernel&m=130833638508657&w=2
> But it doesn't apply anymore and after fixing a trivial merge conflict, it
> fails to build, which is also trivially fixed. Please, add my
>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>

So I guess we can finally solve this issue, thanks.

On the other hand I just noticed the original patch didn't have Bruno's
Signed-off and a commit message was missing. So may I ask you, Bruno, to add
your Signed-off or preferably resend the version tested by Guennadi in the
appropriate patch format.

Thanks,

Florian Tobias Schandinat

>
> to the set and use this updated version:
>
> diff --git a/drivers/video/sh_mobile_hdmi.c b/drivers/video/sh_mobile_hdmi.c
> index 7d54e2c..647ba98 100644
> --- a/drivers/video/sh_mobile_hdmi.c
> +++ b/drivers/video/sh_mobile_hdmi.c
> @@ -1111,6 +1111,7 @@ static long sh_hdmi_clk_configure(struct sh_hdmi *hdmi, unsigned long hdmi_rate,
> static void sh_hdmi_edid_work_fn(struct work_struct *work)
> {
> struct sh_hdmi *hdmi = container_of(work, struct sh_hdmi, edid_work.work);
> + struct fb_info *info;
> struct sh_mobile_hdmi_info *pdata = hdmi->dev->platform_data;
> struct sh_mobile_lcdc_chan *ch;
> int ret;
> @@ -1123,8 +1124,9 @@ static void sh_hdmi_edid_work_fn(struct work_struct *work)
>
> mutex_lock(&hdmi->mutex);
>
> + info = hdmi->info;
> +
> if (hdmi->hp_state == HDMI_HOTPLUG_CONNECTED) {
> - struct fb_info *info = hdmi->info;
> unsigned long parent_rate = 0, hdmi_rate;
>
> ret = sh_hdmi_read_edid(hdmi, &hdmi_rate, &parent_rate);
> @@ -1148,42 +1150,45 @@ static void sh_hdmi_edid_work_fn(struct work_struct *work)
>
> ch = info->par;
>
> - console_lock();
> + if (lock_fb_info(info)) {
> + console_lock();
>
> - /* HDMI plug in */
> - if (!sh_hdmi_must_reconfigure(hdmi) &&
> - info->state == FBINFO_STATE_RUNNING) {
> - /*
> - * First activation with the default monitor - just turn
> - * on, if we run a resume here, the logo disappears
> - */
> - if (lock_fb_info(info)) {
> + /* HDMI plug in */
> + if (!sh_hdmi_must_reconfigure(hdmi) &&
> + info->state == FBINFO_STATE_RUNNING) {
> + /*
> + * First activation with the default monitor - just turn
> + * on, if we run a resume here, the logo disappears
> + */
> info->var.width = hdmi->var.width;
> info->var.height = hdmi->var.height;
> sh_hdmi_display_on(hdmi, info);
> - unlock_fb_info(info);
> + } else {
> + /* New monitor or have to wake up */
> + fb_set_suspend(info, 0);
> }
> - } else {
> - /* New monitor or have to wake up */
> - fb_set_suspend(info, 0);
> - }
>
> - console_unlock();
> + console_unlock();
> + unlock_fb_info(info);
> + }
> } else {
> ret = 0;
> - if (!hdmi->info)
> + if (!info)
> goto out;
>
> hdmi->monspec.modedb_len = 0;
> fb_destroy_modedb(hdmi->monspec.modedb);
> hdmi->monspec.modedb = NULL;
>
> - console_lock();
> + if (lock_fb_info(info)) {
> + console_lock();
>
> - /* HDMI disconnect */
> - fb_set_suspend(hdmi->info, 1);
> + /* HDMI disconnect */
> + fb_set_suspend(info, 1);
>
> - console_unlock();
> + console_unlock();
> + unlock_fb_info(info);
> + }
> }
>
> out:
>
> Thanks
> Guennadi
>
>>
>>
>> Regards,
>>
>> Florian Tobias Schandinat
>>
>>
>> On 06/18/2011 09:19 AM, Bruno Prémont wrote:
>>> Guennadi, could you have a look at (completely untested) patch which avoids
>>> possible deadlock due to inverted lock taking order on hotplug as well
>>> as "readding" lock_fb_info() for fb_set_suspend() call after Herton's
>>> patch to fb_set_suspend().
>>>
>>> Thanks,
>>> Bruno
>>>
>>>
>>> On Sat, 18 June 2011 Bruno Prémont <bonbons@linux-vserver.org> wrote:
>>>> On Fri, 17 June 2011 Florian Tobias Schandinat <FlorianSchandinat@gmx.de> wrote:
>>>>> From: Herton Ronaldo Krzesinski <herton@mandriva.com.br>
>>>>>
>>>>> A lock ordering issue can cause deadlocks: in framebuffer/console code,
>>>>> all needed struct fb_info locks are taken before acquire_console_sem(),
>>>>> in places which need to take console semaphore.
>>>>>
>>>>> But fb_set_suspend is always called with console semaphore held, and
>>>>> inside it we call lock_fb_info which gets the fb_info lock, inverse
>>>>> locking order of what the rest of the code does. This causes a real
>>>>> deadlock issue, when we write to state fb sysfs attribute (which calls
>>>>> fb_set_suspend) while a framebuffer is being unregistered by
>>>>> remove_conflicting_framebuffers, as can be shown by following show
>>>>> blocked state trace on a test program which loads i915 and runs another
>>>>> forked processes writing to state attribute:
>>>>>
>>>>> Test process with semaphore held and trying to get fb_info lock:
>>>>
>>>> ...
>>>>
>>>>> fb-test2 which reproduces above is available on kernel.org bug #26232.
>>>>> To solve this issue, avoid calling lock_fb_info inside fb_set_suspend,
>>>>> and move it out to where needed (callers of fb_set_suspend must call
>>>>> lock_fb_info before if needed). So far, the only place which needs to
>>>>> call lock_fb_info is store_fbstate, all other places which calls
>>>>> fb_set_suspend are suspend/resume hooks that should not need the lock as
>>>>> they should be run only when processes are already frozen in
>>>>> suspend/resume.
>>>>
>>>> From a quick look through FB drivers in 2.6.39 I've found one that would need
>>>> more work:
>>>> - drivers/video/sh_mobile_hdmi.c: sh_hdmi_edid_work_fn()
>>>> Should get changed to
>>>> a) right locking order in case (hdmi->hp_state == HDMI_HOTPLUG_CONNECTED)
>>>> b) lock fb_info in the other case
>>>> For this one fb_set_suspend() does get call in a hotplug worker,
>>>> thus independently on suspend/resume process.
>>>>
>>>> The rest does match the suspend/resume hook pattern mentioned.
>>>>
>>>> Bruno
>>>>
>>>>
>>>>> References: https://bugzilla.kernel.org/show_bug.cgi?id=26232
>>>>> Signed-off-by: Herton Ronaldo Krzesinski <herton@mandriva.com.br>
>>>>> Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
>>>>> Cc: stable@kernel.org
>>>>> ---
>>>>> drivers/video/fbmem.c | 3 ---
>>>>> drivers/video/fbsysfs.c | 3 +++
>>>>> 2 files changed, 3 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
>>>>> index 5aac00e..ad93629 100644
>>>>> --- a/drivers/video/fbmem.c
>>>>> +++ b/drivers/video/fbmem.c
>>>>> @@ -1738,8 +1738,6 @@ void fb_set_suspend(struct fb_info *info, int state)
>>>>> {
>>>>> struct fb_event event;
>>>>>
>>>>> - if (!lock_fb_info(info))
>>>>> - return;
>>>>> event.info = info;
>>>>> if (state) {
>>>>> fb_notifier_call_chain(FB_EVENT_SUSPEND, &event);
>>>>> @@ -1748,7 +1746,6 @@ void fb_set_suspend(struct fb_info *info, int state)
>>>>> info->state = FBINFO_STATE_RUNNING;
>>>>> fb_notifier_call_chain(FB_EVENT_RESUME, &event);
>>>>> }
>>>>> - unlock_fb_info(info);
>>>>> }
>>>>>
>>>>> /**
>>>>> diff --git a/drivers/video/fbsysfs.c b/drivers/video/fbsysfs.c
>>>>> index 04251ce..67afa9c 100644
>>>>> --- a/drivers/video/fbsysfs.c
>>>>> +++ b/drivers/video/fbsysfs.c
>>>>> @@ -399,9 +399,12 @@ static ssize_t store_fbstate(struct device *device,
>>>>>
>>>>> state = simple_strtoul(buf, &last, 0);
>>>>>
>>>>> + if (!lock_fb_info(fb_info))
>>>>> + return -ENODEV;
>>>>> console_lock();
>>>>> fb_set_suspend(fb_info, (int)state);
>>>>> console_unlock();
>>>>> + unlock_fb_info(fb_info);
>>>>>
>>>>> return count;
>>>>> }
>>>
>>>
>>> diff --git a/drivers/video/sh_mobile_hdmi.c b/drivers/video/sh_mobile_hdmi.c
>>> index 2b9e56a..b1a13ab 100644
>>> --- a/drivers/video/sh_mobile_hdmi.c
>>> +++ b/drivers/video/sh_mobile_hdmi.c
>>> @@ -1151,27 +1151,27 @@ static void sh_hdmi_edid_work_fn(struct work_struct *work)
>>>
>>> ch = info->par;
>>>
>>> - console_lock();
>>> + if (lock_fb_info(info)) {
>>> + console_lock();
>>>
>>> - /* HDMI plug in */
>>> - if (!sh_hdmi_must_reconfigure(hdmi) &&
>>> - info->state == FBINFO_STATE_RUNNING) {
>>> - /*
>>> - * First activation with the default monitor - just turn
>>> - * on, if we run a resume here, the logo disappears
>>> - */
>>> - if (lock_fb_info(info)) {
>>> + /* HDMI plug in */
>>> + if (!sh_hdmi_must_reconfigure(hdmi) &&
>>> + info->state == FBINFO_STATE_RUNNING) {
>>> + /*
>>> + * First activation with the default monitor - just turn
>>> + * on, if we run a resume here, the logo disappears
>>> + */
>>> info->var.width = hdmi->var.width;
>>> info->var.height = hdmi->var.height;
>>> sh_hdmi_display_on(hdmi, info);
>>> - unlock_fb_info(info);
>>> + } else {
>>> + /* New monitor or have to wake up */
>>> + fb_set_suspend(info, 0);
>>> }
>>> - } else {
>>> - /* New monitor or have to wake up */
>>> - fb_set_suspend(info, 0);
>>> - }
>>>
>>> - console_unlock();
>>> + console_unlock();
>>> + unlock_fb_info(info);
>>> + }
>>> } else {
>>> ret = 0;
>>> if (!hdmi->info)
>>> @@ -1181,12 +1181,15 @@ static void sh_hdmi_edid_work_fn(struct work_struct *work)
>>> fb_destroy_modedb(hdmi->monspec.modedb);
>>> hdmi->monspec.modedb = NULL;
>>>
>>> - console_lock();
>>> + if (lock_fb_info(info)) {
>>> + console_lock();
>>>
>>> - /* HDMI disconnect */
>>> - fb_set_suspend(hdmi->info, 1);
>>> + /* HDMI disconnect */
>>> + fb_set_suspend(hdmi->info, 1);
>>>
>>> - console_unlock();
>>> + console_unlock();
>>> + unlock_fb_info(info);
>>> + }
>>> pm_runtime_put(hdmi->dev);
>>> }
>>>
>>> --
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>>>
>>
>
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/
>